1. Field of the Invention
This invention relates broadly to electrical switching circuits. More particularly, this invention relates to electrical switching circuits that utilize one or more electromechanical relays.
2. State of the Art
Electromechanical relays are a very mature technology. Despite being replaced by semiconductor devices in many applications, the basic relay still retains many advantages over modern switching systems including an inherently low voltage drop and electrical isolation.
The life of the electrical contacts of the relay is usually the limiting factor in determining their incorporation in modern circuits. This is especially true for direct current (DC) applications, where contact erosion takes place. The rated useful life of the relay contacts is often only 1% of the mechanical life, especially where loads which are controlled are inductive (e.g., motor), or have a high in-rush current (e.g., tungsten lamps).
Relays are still widely used in automotive applications as the system voltage for automobiles is relatively low e.g. 12V. At higher voltages, the material from which the relay contacts are made behave differently and contact erosion through arcing during the opening and closing of the contacts becomes more significant. This has for instance been a major hurdle in 42V systems.